How babies come out

I'm pregnant with my second baby. My son is four and my friends daughter will be five next month. They were talking about how the baby comes out and my son asked me how they came out. I told him and he said that Hanna told him that when it's time the girl has to push really hard on her knees and then the baby will come out. I thought that was pretty well thought out considering when you watch something on TV like a baby story they usually show the women holding her knees up and that could totally come across as pushing on the knees.